Ships and barges, and the marine structures built to accommodate them, typically weigh many thousands of tons, even when not loaded with freight or other cargo, and the ships move at speeds often in excess of 20 knots. Yet they are typically fabricated of steel plates less than a quarter of an inch thick. They have all increased considerably in size and power over just the last six years. A new breed of ship docking modules, tractor tugs and reverse tractor tugs being built have increased horsepower, increased maneuverability (due in part to the 360 degree rotatable propeller and the Voith Schneider "Beater" propulsion technology), and increased thrust.
The days of conventional tugs with one or two fixed propellers are closing, leaving this antiquated design relatively ineffective in today's market because they cannot be multifunctional. The new tugs on the other hand are considerably more expensive than their predecessors, and they must work more for their owners to make money. The tugs work more by being more versatile. For example, the new breed of tug must be able to perform ship assist, barge tendering, piloting, and logging functions. The increased horsepower, maneuverability and thrust allow these tugs to do all of that.
As tugs, barges and ships increase in size, so do the onshore marine structures which provide berthing. More sophisticated renderings are required on these structures in order to provide safe operation and maximum performance. Similarly, trailers for large trucks typically weigh many thousands of pounds and move at speeds upward of seventy miles per hour, but are made of aluminum sheet less than one tenth of an inch thick. Tugboats have thick, reinforced bows and sterns, and loading docks are generally made of solid, steel-reinforced concrete. The size and weight of automobiles, and the kinetic energy involved in their movement, are correspondingly large, while support columns in parking garages are for all practical purposes rigid, yet at the same time brittle. Thus for many years designers have struggled with the problem of dissipating the forces and energies associated with the impact and rubbing of large, relatively thin-skinned, generally moving structures against relatively solid or monolithic obstacles. Among the difficulties encountered have been the stiffness, weight, cost, durability, and energy-absorption, or dampening, capacities of available designs.
Several approaches to the problems outlined above have appeared. For years fenders fabricated from filled rope bundles have been used on tugboats, with some success. Improved performance has been provided by such fenders as, for example, built-up composite bow bumpers for tugs and other boats, fabricated of rubber or similar materials. Such bumpers have given adequate service under a wide variety of conditions. Still other suggestions have included the use of bagged buoyant materials, the use of entire automobile tires lashed or mounted in place on the collision-bearing surface, and whole circumferential sections of automotive tires strung together on blocks or trussed together with auxiliary structure and fasteners in something like the manner of teeth on an old necklace. However, each of these solutions has to some degree fallen short of the requirement for a selectably soft, durable, simple, inexpensive, and highly adaptable general use fender.
The built-up rubber composite bumper of U.S. Pat. No. 3,063,399 to Schuyler (the text of which is hereby incorporated by reference as if fully set forth) has been found to be relatively stiff in some applications, and in some instances to have prevented less damage than might have been desired. Furthermore, the physical properties (such as deflection under load and energy absorption) are relatively static because the construction method cannot be altered to engineer a broad range of deflection and energy absorption values for the many varying circumstances in which such devices will be employed. Conventional composite fender constructions also exhibit a rather low coefficient of friction, notwithstanding the Schuyler '399 patent's disclosure of a kind of "squeegee" action. Such low friction is generally undesirable in situations where holding ability, or "stiction", as the term is generally known in the art, is preferred and even sometimes required for safe and efficient operation.
One proposed solution to the problem has been the Schuyler Rubber Company Model SR3D fender. The Schuyler SR3D utilizes built-up aggregations of same size, single-ply rubber bumper loops to increase fender softness. Holding ability in some applications has been increased as well. Holding ability, or "stiction", which is frequently desired in contacts such as those experienced by tugboats pushing on ships or barges, is generally taken in the fender industry to mean resistance to a tangential component of the pushing force, such as that imparted by a tugboat pushing inward and forward on a ship or barge. However, the single ply loops of the SR3D have proved too soft for some applications, and have in some situations shown disappointingly short durability and fatigue lives. That is, they give, or deflect, in relatively large amounts upon initial, relatively light loading, and then "bottom out" suddenly when the single ply loops have fully deformed (colloquially, one might say when they were fully "squashed") onto the relatively harder fender base and spacer materials. They have also shown a tendency to tear or break, either in mid-loop or at the base, under relatively moderate shearing loads, or at the base under repeated full deformations. The use of same size loops similarly limits design variability in creating shield and dampening structures such as marine fenders.
The single ply of the SR3D loops also does not allow one to engineer a fender or series of fenders to exhibit the varying degrees of load deflection, energy absorption, and "stiction" required of the majority of current fendering applications. The SR3D also does not allow the gaps between a series of fenders to be eliminated as desired, where it is generally preferred to have no gap at all in such a series.
At the same time, the world has become subject in recent years to increasingly harsh requirements for the efficient utilization of resources. Landfills are becoming huge, seemingly insolvable environmental blights, the pollution caused by the chemical processes associated with the production of thousands of items costs billions of dollars each year to mitigate, and the waterways of the world are being filled with trash and poisons. In particular, chemical processes used in the production of metals and polymers such as those used in automobile tires have been seen as damaging, and disposal of the automobile tires (and the like) themselves, once they have been used and discarded, has become a difficulty of its own peculiar dimension. Hundreds of millions of tires are discarded each year in the United States alone. Landfills, already filled to overflowing, have refused to accept more of them; and special tire dumps, filled with millions of discarded tires, have spontaneously combusted and burned for months in fires so hot and dangerous as to defy control by any reasonable firefighting techniques. And tires do not biodegrade.
Thus there are independent needs for a selectably soft (or stiff), engineerable, durable, simple, inexpensive, and highly adaptable general use fender having good holding ability and not prone to tearing or base failure under shear or repeated direct loads; and efficient, cost effective ways of reusing discarded materials, in particular used truck and bus tires. There thus exists a definite need for a new fendering system that will: provide more cushion than would be available from the solid laminated, extruded, or molded rubber products currently available; provide greater and selectably greater stiffness and rigidity than the Schuyler SR3D; provide more durability than the Schuyler SR3D so that the longer useful life of the new fender system makes it more economical, durabilities approaching and even exceeding the solid laminated models now in use; and provide an engineerable system to achieve variable and selectable degrees of softness, durability, and stiction.